I am using Picoscope 6.3.55.0 & 3224 hardware to capture turnoff waveforms, using both simple edge & advanced edge with hysterisis to trigger off the digital control signal rising edge of ch1, I also get triggers when the other channel 2 rising edge coincides (within nom. 300uS window) with the digital signal falling edge. So its capturing some turnons as well.Ch2 is a current measurement across 1 ohm of a nominal 280mA load (250mA resistive, 29mA LED PFC Lamp operating off 110V 50hz AC.The 110V supply is transformer isolated , the Logic board is Earthed & the Laptop is running off battery so there are no ground loops to interfere.

I dont miss any turnoffs, just get additional unwanted waveforms in the buffer (for later analysis & evidence)

We cannot setup the same experiment as you, as it is not a recommended way to measure such voltages. It looks like you are probably getting some sort of coupling. I would recommend using something like a differential oscilloscope probe.

You might be right, there is probably enough parasitic capacitance in the isolating transformer & my setup to affect the 3224.

The logic circuit actually is not earthed as I stated, it is powered from a topward dc bench supply & Vicor DC-DC converters so has double isolation from the mains supply.(but is sitting on the bench in metal frame) .The laptop is mounted on an insulating base.

We have a job coming up soon where we should be able to purchase an isolated differential probe. I will repeat the test & advise results.